Hey Kenton..lots to talk about!
“This is precisely the problem I had yesterday sparring with my JiuJutsu friend. I couldn’t get inside or passed his elbows because he kept moving around and backing up. And then if by chance I got in…if I got in too close, he would clinch to takedown to rolling on the ground BJJ!”
***IN MY OPINION, the best way to go is to punch/kick your way in with boxing type straight leads, low front kicks, low roundhouse kicks - and other “boxing/kickboxing type moves” until you’ve got limb-to-limb contact (unless you’ve already knocked him down with one of your punches or kicks
)…and then use your wing chun infighting strikes/traps/sweeps, etc.
As to getting inside his elbows…if he’s preventing that then work from outside his leading elbow - but always trying to stick and pressure in order to take his space away - while hitting without getting hit back - if possible.
If he goes for a takedown - you need to develop some solid wrestling sprawls and other anti-takedown moves - as well as some wrestling/grappling pummeling to clinch…and some nice Thai elbows and knees from the clinch could be a welcome addition to your arsenal also.
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“I also noticed that it just wasn’t a matter of squaring up my centreline and stepping in to striking distance…I had to get my head (and torso) inside/passed his elbows as well…which is tricky while he’s throwing a nice head-ringing hook.”
***YOU SHOULD LOOK INTO the use of sidestepping with biu/lop against hook punches (as it is found in TWC).
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“It’s funny that the thread has gone this way, because this is something that I’m struggling with…Finding that balance between ranges within my Wing Chun.”
***WELCOME TO THE CLUB! 
Hint: Wing Chun is a close range striking/kicking art - and very little else. (See above about the longer ranges).
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“Plus, I find I can’t block EVERYTHING that he’s throwing. I’m better to move around, back up, whatever…not what I’ve been taught! Always been taught to drive forward…but you should have seen my head snap back when I stepped in to close that gap.”
***TWO THINGS about this, imo…Learn to watch the elbows and knees and you’ll get hit less - and forget all the B.S. about never moving back.
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“It’s almost like I’m going more the boxing route right now while trying to adapt my Wing Chun to a sparring session.”
***A BOXING FRAMEWORK (along with low kicks) as a delivery system for your close range wing chun is the way to go, imo.
And speaking of that, KPM/Keith had this to say:
“So here’s the ‘dirty little secret’ that a lot of Wing Chun people don’t talk about. In order to make their Wing Chun work in a sparring situation, they have to ‘box’ with it! But the problem is that very few do it well because they don’t spend much if any training time developing the skills and attributes needed to ‘box’ well. Instead they spend the majority of training time learning forms and doing Chi Sau.”
***ABSOLUTELY RIGHT ON THE MONEY!
…
"IMHO, our Wing Chun ancestors did very little if any ‘sparring.’ That’s not to say that they didn’t go out and fight! But sparring is not fighting. As we put on protective equipment and spar, we create a new environment that forces some changes. If you try to force "traditional/original/whatever-you-want-to-call-it Wing Chun into this new environment without embracing those changes that are needed, it is never going to work well. That’s one of the reasons you don’t see Wing Chun guys excelling in combat sports…they are all a ‘sparring’ environment.
***BINGO AGAIN! (This guy’s on a roll.
)
But here comes his best stuff:
“Why is this loose boxing ‘structure’ the predominant thing you see in just about every form of competitive stand-up fighting such as western boxing, modern thai boxing, american kickboxing, and san shou? Maybe it is because this looser structure flows more naturally while still providing an effective platform under pressure. When it comes right down to it, performance rules over precision.”
***IT’S ABOUT THE FLOW. Real fighting/sparring is about constant movement..give-and-take…in-and-out…side-to-side…always looking for angles to go in and attack on. And if you’re a wing chun guy - you stay in and go forward as long as you can - but always remain ready to let that strategy go if you’re no longer in the very close range - or if you don’t have enough control over his ability to strike/kick/grab your body.
And as for going in with “mon sao”…forget it.
Go in with longer range straight lead punches like boxers do - rotating the lead shoulder, and the hip, pushing off the feet with a little bounce in your step, etc. (Maybe even an occasional lead hook punch, a rear cross, a straight lead/rear cross combo, etc.)
In other words, learn a little boxing! 